Machines of a domestic or semi-professional type are known, wherein the container where the ice-cream is formed cooperates with a mixing blade and with means to transfer the cold, or heat absorption means.
The mixing blade takes motion from drive means associated with the cover.
According to a variant, the blade takes motion from drive means located under or at the side of the container and connected to the mixing blade by a drive shaft which passes axially to the container with a cylindrical design. The drive means can be electric or manually driven.
This type of machine, in relation to the chain of cold, has developed different design philosophies in terms of the cooperation of the heat absorption means with the container of the products which are transformed into ice-cream.
A first design philosophy provides a fixed evaporator coil, that is, a coil wherein the temperature of the compressed gas goes down as it expands, which is cylindrical in shape; the coil surrounds the container and leaves an interspace between the coil and the container for the operations to insert and remove the container itself.
This type of solution does not achieve an optimum heat exchange between the coil and the container, given the ring of air which, in fact, is greatly insulating.
To improve the transfer of cold, it was then provided to fill, on each occasion, the ring of air with alcohol or other liquid which does not freeze at the normal working temperatures of the machine.
Apart from the ever-present danger of fire, it is certainly not easy or simple to insert the container into a bath of alcohol. Moreover, there is always the danger of overflow.
A second design philosophy has conceived of an elastic evaporator coil equipped with clamping means, as shown for example in U.S. Pat. No. 4,573,329 and in EP-A-129.706. By acting on the clamping means the evaporator coil opens or closes radially, so that it is possible to insert (or remove) the container by extracting it axially from the coil. When the container is inserted into the evaporator coil, the clamping means are activated and the evaporator coil contracts radially, surrounding, and closely connecting with, the peripheral cylindrical body of the container.
This system guarantees an optimum heat absorption, but it has the drawbacks of the high cost of the evaporator coil and of the fact that it is easily damaged even by a careful user, and even more so by an inattentive user.
Damage to the coil can also entail a dispersion into the environment of dangerous refrigeration gases.
A system is also known, from JP-A-02-145153 and from JP-A-02-100634, which provides that it is the container that is pressed elastically against the rotating mixing blade, by a coil located below. The fact that the inside of the container and the mixing blade are held pressed against each other is important in order to prevent the formation of ice in the cooled zone, as any formation of ice would reduce the heat exchange.
However, the solution described in the Japanese documents indicated above entails problems of safety and correct exploration of the cooled bottom.
Applicant therefore set himself the problem of finding an optimum solution to these problems and surprisingly found, and also studied, experimented and embodied the present invention.